The invention concerns a system having an air-mass meter for an internal combustion engine in which the measurement place of an air-mass meter is located in a measurement tube.
For the regulating of internal combustion engines with fuel injection, it is necessary to measure the mass of air drawn in by the engine. Mechanical systems for this purpose are known which operate, for instance, with movable flaps or aperture plates which extend into the stream of air. Sensors are also known, for instance hot-wire air-mass meters, for the measurement of the mass of air. They have the advantage that they have no moving, parts and interfere less with the flow of air than the mechanical systems do. Furthermore, the result of the measurement is independent of differences in altitude, which is not true of the mechanical systems, which primarily measure the quantity of air.
Various different methods have been employed for the arrangement of the air-mass or air-quantity meters. Thus it is known, for instance, to arrange an air-mass meter operating by ultrasonics within an air filter. In this case, the measurement place of the air-mass filter is so arranged within a measurement tube that the air flowing within the air filter moves over the outside of the measurement tube in the region of the measurement place. In this way assurance is had that the measurement tube substantially assumes the temperature of the air drawn in, which, in its turn, is of essential importance for the operation of the air-mass ultrasonics meter. The known construction adapted to an air-mass meter operating by ultrasonics has, however, structural disadvantages and, for instance, does not assure a sufficient damping of pulsations of the air or of the air/fuel mixture within the intake channel.